I like to play Magic: The Gathering, and I'm interested in calculating the probability of certain things in the game.
After drawing 7 cards from a 60 card deck, what is the probability that draw will contain at least one of x, where x is a card having y copies?
My best effort has been with the following formula:
$$ \binom{y}{1}\binom{60 - y}{6}/\binom{60}{7} $$
There are deck analyzers that will generate the answer for a simple 7-card draw (I'm wanting to get the formula though). Our answers are the same for y=1, but they start to deviate for y=2, y=3, etc. which has put some doubt in this formula.
What's the proper way to solve this?